Method for drying articles having a low heat tolerance

ABSTRACT

A method for drying articles having a low heat tolerance, such as parachutes fabricated of synthetic fibers, comprising the steps of first heating a hermetically sealable chamber to a predetermined temperature which the article can tolerate, then evacuating the chamber to create a vacuum therein for substantially reducing the boiling-point of any moisture in the article, and exhausting the boiled-off moisture to complete the drying cycle.

United States Patent Ramsay 4] METHOD FOR DRYING ARTICLES HAVING A LOWHEAT TOLERANCE [72] Inventor: James M. Ramsay, Yuma, Ariz,

[73] Assignee; The United States of America as represented by theSecretary of the Navy '22 Filed: March 29, 1971 [2]] Appl. No.2 129,062

Related us. Application Data [62] Division of Ser. No. 861,104, Sept.25, 1969,

Pat. No. 3,605,278.

[52] US. Cl ..34/15, 34/92 [51] Int. Cl ..F26b 5/04 [58] Field of Search..34/15, 92, 103, 104

[5 6] References Cited UNITED STATES PATENTS 3,615,310 10/1971 Long..34/92 1 Oct. 17, 1972 3,057,078 l0/1962 Gold.. ..34/92 FOREIGN PATENTSOR APPLICATIONS 1,378,202 10/1964 France ..34/15 18,018 8/1912 GreatBritain ..34/15 Primary Examiner-Frederick L. Matteson AssistantExaminerW. C Anderson Attorney-R. S. Sciascia, George J. Rubens and J.W; McLaren [s7 ABSTRACT' A method for drying articles having a low heattolerance, such as parachutes fabricated of synthetic fibers, comprisingthe steps of first heating a hermetically scalable chamber to apredetermined temperature which the article can tolerate, thenevacuating the chamber to create a vacuum therein for substantiallyreducing the boiling-point of any moisture in the article, andexhausting the boiled-off moisture to complete the drying cycle.

2 Claims, 5 Drawing Figures PATENTEDncr 11 I972 3 6 98 O9 8 SHEET 1 0F 2METHOD FOR DRYING ARTICLESHAVING A LOW HEAT TOLERANCE CROSS-REFERENCE TORELATED APPLICATIONS The invention is a divisional application of Ser.No.

861,104 filed on Sept. 25, 1969, now U.S. Pat. No. 3,605,278.

STATEM ENT OF GOVERNMENT INTEREST The invention described herein may bemanufactured and used by or for the Government of the United States ofAmerica for governmental purposes without the payment of any royaltiesthereon or therefor.

BACKGROUND OF THE INVENTION I paratus has contributed to malfunctioningof deployed parachutes. This malfunctioning occurs when a damp parachuteis repacked, flown to a high altitude where it freezes, and theparachute is again deployed on landing before it has the opportunity todefrost. The accepted standard for the amount of humidity in a parachuteis 5 percent of the dry weight, and if the humidity is at this level orless, the parachute can be repacked. The problem of adequately dryingparachutes has long been a problem in the U.S. Naval Serviceparticularly on board aircraft carriers where available space fortowertype drying is limited and costly. Conventional clothes dryingmethods all have serious limitations. Because of the low heat toleranceof nylon, being the conventional parachute material, hot air drying istime consuming and inefficient especially where the ambient air is hotand humid. Dehumidification does not work efficiently were it is coldand humid. Tests have indicated that the combination of tumbling theparachute with an air flow is not satisfactory because the fibersseparate and give the parachute a nap-like angora.

Although prior art devices have allegedly used vacuum techniques inassociation with heat for drying purposes, the vacuum was used solely asa suction means to draw off the moistened air from the drying chamberinto which ambient air was introduced during the drying process.

SUMMARY OF THE INVENTION The problem of drying an article, such as aparachute, has beensolved by employing a method using a high vacuum forboiling-off the moisture without the requirements of tumbling,circulating hot air, or relying on ambient air or other climaticconditions. The parachute is inserted into a stationary, hermeticallysealed chamber which is then heated to a temperature that the articlecan tolerate. The heating is preferably supplied by a flexible blanketinside the chamber into which the article is folded back-andforth, andby an external blanket around the chamber, if needed. The chamber isthereafter subjected to a substantially high vacuum, preferably, thehighest vacuum that is obtainable from commercially available pumpequipment, which is about 29.5 inches Hg. With such a vacuum, theboiling point of the moisture in the parachute can be reduced to about60 F. Obviously, the higher the parachute can be heated safely over theboiling point of the moisture, the quicker the article can be dried. Forexample, with the chamber heated to 125 F., and a vacuum of 29.5 inchesHg a normal drying cycle will comprise a 10 minute heat build-up, a 25minute vacuum phase, and a 5 minute pressure dump and cool-down phase.The latter phase dissipates the vacuum in the chamber to permit accessto the chamber, and cooling of the parachute to a handling temperature.The length of the heat phase, vacuum phase, and cool phase can bemanually or automatically varied in length and is controlled by a timerin an electrical circuit. I

STATEMENT OF THE OBJECTS OF THE INVENTION A principal purpose of theinvention is to provide a method for drying articles having a low heattolerance quickly, effectively, for use in an apparatus occupying aminimum of space making it particularly suitable for shipboard use. I

Another important object of the invention is to provide a drying methodwhich does not require the apparatus to be rotated for tumbling thearticle to be dried and which dies not require the introduction ofambient air into the apparatus during the drying cycle.

Other objects and many of the attendant advantages of this inventionwill be readily appreciated as the same becomes better understood byreference to the following detailed description when considered inconnection with the accompanying drawings.

BRIEF DESCRIPTION or THE DRAWINGS FIG. 1 is a perspective view of dryingapparatus employing the novel method with the chamber partially brokenaway to show the internal heating blanket'in a slightly extendedposition, the parachute being omitted;

FIG. 2 is a side elevation of the drying chamber and pump assembly;

FIG. 3 is a partial elevation in section of the drying apparatusshowingthe internal heat blanket connections; and

FIGS. 4 and 5 are schematic wiring diagrams of a power circuit and acontrol circuit, respectively.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings wherelike reference numerals refer to similar parts throughout the figuresthere is shown in FIG. 1 the vacuum drying apparatus 10 disclosed inapplicants above-identified pending ap plication and now patent number3,605,278 which is designed principally, although not necessarilylimited, to drying articles having a low tolerance to heat and totumbling. An example of articles of this type are parachutes made ofsynthetic fibers, such as nylon. It has been found that a normally wetstandard 28 ft diameter Navy service type parachute contains about 4pounds of water that should be removed. A normally wet parachute isconsidered one that has been subjected to rain. It has been determinedthat when the chamber is maintained at 125 F., 333 cu ft of vapor mustbe off-gassed for each pound of water. To maintain the temperature of125 F. requires an additional heat of 7 1,000 BTUs per pound, regardlessof the degree of vacuum that is to be maintained.

Dryer 10 comprises a drum-shaped chamber 12 fabricated of a tubularmetal side wall 14 having welded thereto a bottom plate 16, and an upperneck collar 18 to which a door 20 is hinged at 22. Door 20 is providedwith an O-ring 24 for sealable contact with collar 18 making the chamberhermetically air tight when closed. In the particular installation beingdescribed because of the high vacuum being employed the chamber isfabricated of heavy plate aluminum, the

side walls being one-eighth inch in thickness, the top door beingfive-eighths inch thick and the bottom plate being 1 inch thick. Becauseof the vacuum being employed no latches are needed to lock the door in aclosed position. The door has a large diameter to provide maximum accessto the chamber for loading and unloading the parachutes which aresomewhat bulky, and to facilitate folding of the parachute within thechamber in a manner to be described. Chamber 12 is supported on a basecabinet 26 having leveling legs 28. A console 29 is mounted on cabinet26 adjacent chamber 12 and contains the operating controls as will bedescribed. Chamber 12 may be heated by an external and internal heatingmeans singly or in combination as the heating requirements may dictate.External heating is performed by an electric blanket 30 which is snuglywrapped externally around chamber 12 and is provided with cutoutportions at 31 to accommodate a heating junction box 32 and otherelements attached to the chamber. An external heater blanket 30a is alsosecured to the bottom surface of plate 16. An'insulating jacket 33 ismounted around the external heater blanket 30 and is held in position bya thingsplit tubular metal shroud'34 held together by a plurality ofbands 36 and fasteners 38. A bottom insulation pad 33a is also providedfor the bottom heater blanket 30a.

A feature of the drying apparatus is the employment of a flexibleinternal heater blanket 40, preferably electrically controlled, whichblanket serves principally to supply the additional heat to theparachute, approximately 4,000 BTU, to maintain the drying temperature.of 125 F. The internal temperature of the chamber is indicated at gauge41 on console 29. In the specific installation herein described thecombined internal and external heat sources have a capacity of 12,000BTU/hr. For a chamber having an internal diameter of 30 inches, internalblanket 40 is dimensioned 22 inches in width and approximately 120inches in length. The internal heater blanket is constructed as flexibleas possible to allow folding to a 1 inch minimum radius, the spacebetween the sides of the blanket and the inside wall of the chamberallowing room for the parachute when folded. The technique of foldingthe parachute back-and-forth within the internal heater blanket ensuresmaximum heating contact as well as providing voids to permit the escapeof the vapor being generated.

As shown in FIG. 3, one end of internal heater blanket 40 is secured toa chamber floor plate 42 by a pair of bolted straps 44. Floor plate 42is secured to bottom plate 16 in spaced relation thereto by bolts 46andspacers 48 providing a sump 50 for any water draining from the wetparachute when initially placed in the chamber. There is no need todrain sump 50 as the moisture will be quickly evaporated when thechamber is subjected to the drying cycle.

lntemal blanket 40 is suitably controlled in automatic or manualoperation by a control circuit to be described, being connected byconductor 51 to receptacle 52 mounted on the chamber wall and groundedby strap 54 (FIG. 2). The openings through chamber 12 for the electricalconnections are sealed by epoxy so that the installation is heliumtight.

As previously described, the chamber is subjected to a very high vacuumto reduce substantially the boiling point of the moisture in theparachute and, of course, the more perfect the vacuum the quicker thedrying cycle. For example, it has been found that the boiling point ofthe moisture can be reduced to 30 F. when the chamber is subjected to avacuum of 29.8 inches Hg, whereas the boiling point increases to 105 F.when a vacuum of 27.8 inches Hg is employed. However, for thecontemplated use of drying parachutes the employment of exotic equipmentto obtain the highest vacuum is not considered warranted. The bestresults that can be obtained with present day commercially availableequipment achieves the operating vacuum of about 29.5 inches Hg whichreduces the boiling point of the water in the parachutes to about 60 F.The equipment employed in the described installation includes a 10 HPmotor 56 which drives a 200 cfm pump 58 having a muffler 60 to keep thenoise level at 55 db or lower. The pump is connected to chamber 12 via a3 inch flexible pipe 62 and through a solenoid operated vacuum valve 64and outlet 66 which controls the vacuum in chamber 12 and the dumping ofthe vapor being formed. A direct reading vacuum gauge 67 is convenientlymounted in the front of the chamber 12.

A guard plate 68 is welded tothe inside of chamber 12 in spaced relationto outlet 66 to prevent the parachute from accidentally blocking theoutlet when folded into the chamber, (FIG. 1). After the completion ofthe vacuum drying cycle, the chamber is relieved of the vacuum by asolenoid operated pump valve 70 mounted to chamber 12 (FIG. 2).

The various valves and heating elements in the drying apparatus areoperated in a controlled circuit and a controlling circuit having commonrelays, and the circuits are separately illustrated for clarity. The220V power circuit is diagrammatically illustrated in FIG. 4, being thecontrolled circuit, and-the 1 10V controlling circuit isdiagrammatically illustrated in FIG. 5. Referring to FIG. 4, linevoltage of 220V (3 phase, 20 amp) is connected through suitable circuitbreakers 72 across resistance-type heating elements 74, 76, and 78 ofthe internal, external and bottom heater blankets 40, 30, and30a,'respectively. Each line to the respective heating elements areprovided with suitable thennostatic relay switches 80, 82, and 84, eachrelay being a double-pole double-throw type and preset to limit itsrespective blanket to a predetermined temperature and controlled inoperation by the control circuit in FIG. 5. Solenoid operated vacuumvalve 64 and dump valve 70 are separately connected in parallel acrossthe line voltage, and each are provided with a relay switch 86 and 88,respectively.

The control circuit in FIG. 5 is also connected to 220V line voltagethrough a step-down transformer 90 which reduces the 220V line voltageto 110V. A fuse 91 protects the control circuit. The control circuitincludes three toggle switches 92, 94, and 96 arranged in parallelcircuits for controlling the power circuits to the heaters, and thecircuits including the vacuum valve and the dump valve, respectively.Each toggle switch has three positions, namely, AUTOMATIC, MANUAL, andOFF. A timer 98 (0-60 minute scale) is connected to each AUTOMATICposition of the switches for automatically controlling the operation ofthe various respective circuit components in accordance with theselected cycle. The MANUAL position of each toggle switch is connectedin the control circuit in a manner to by-pass the timer to permit manualoperation of the individual components when desired.

As is apparent from the drawings, the solenoid portions for the variousrelay switches in the power circuit of FIG. 4 are located in the controlcircuit of FIG. 5. Heater switch 92 controls the three parallel heatercircuits. The internal heater circuit includes relay 80 and a variabletemperature control 100 (0300 F.) which permits a manual mode of theinternal heater. The external heater control circuit includes relay 82and a variable temperature control switch 102, while bottom heatercontrol circuit includes relay 84 and a variable control switch 104.Likewise, the vacuum valve toggle 3 switch 94 includes solenoid 86, anddump valve toggle switch includes solenoid 88.

As previously stated, one drying cycle that has been found to worksatisfactorily for drying standard parachutes includes a minute heatbuild-up stage by the various heater elements to achieve a 125 F.temperature in the drying chamber which is thereafter maintained by thethermostatic controls. Normally, it is not desirable to commenceevacuating the chamber prior to the heat build-up phase because it wouldbe more difficult and take much longer time to reach the desiredtemperature of 125 F. After the heat build-up stage, a minute vacuumphase is commenced. During the vacuum stage the internal heater is oneprimarily involved in maintaining the 125 F. temperature to replace theheat lost in evaporation. Obviously, the internal heater is cycled moreoften during the initial vacuum stage. After the vacuum phase a 5 minutedump phase is initiated in which the dump valve is operated to admitambient air into the chamber to dissipate the vacuum and to cool theparachute to permit the chamber to be opened and the parachute removed.

The various valves for the vacuum, temperature and phase duration of theheating cycle heretofore described are intended to be only illustrative,and may vary depending on the specific article to be dried and theamount of moisture to be removed.

The novel method satisfies a long-felt requirement for drying articlesquickly and efficiently, especially articles that cannot tolerate highdrying temperatures. The drying operation is achieved without the needfor moving parts in the chamber, the use of ambient air, or the need forblowers which might otherwise damage sensitive fabrics. These resultsare achieved by the use of a high vacuum and the unique arrangement ofheater elements, particularly the flexible internal heater, to enablethe removal of moisture in the article by a boilin E rocess.

%)%vi usly many modifications and variations of the present inventionare possible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

What is claimed is: 1. A method of drying a parachute fabricated ofsynthetic fibers having a lowheat tolerance comprising 0 the steps of:

inserting the parachute in a chamber;

first heating the chamber to a predetermined temperature between 60 toF. below which the article can tolerate;

evacuating said chamber to create a vacuum of between 27 inches Hg to29.5 inches Hg therein for substantially reducing the boiling-point ofany moisture in said article;

exhausting the boiled-off vapor from said chamber until the article isdry;

relieving the vacuum within the chamber to complete the drying cycle.

2. The method of claim 1 wherein the heating is achieved by external andinternal means, the latter by folding the article within a flexibleelectric blanket position within the chamber.

1. A method of drying a parachute fabricated of synthetic fibers havinga low heat tolerance comprising the steps of: inserting the parachute ina chamber; first heating the chamber to a predetermined temperaturebetween 60* to 140* F. below which the article can tolerate; evacuatingsaid chamber to create a vacuum of between 27 inches Hg to 29.5 inchesHg therein for substantially reducing the boiling-point of any moisturein said article; exhausting the boiled-off vapor from said chamber untilthe article is dry; relieving the vacuum within the chamber to completethe drying cycle.
 2. The method of claim 1 wherein the heating isachieved by external and internal means, the latter by folding thearticle within a flexible electric blanket positioned within thechamber.